In order to obtain the approximately or substantially maximum output from a permanent magnet type electric power generator connected to a windmill or waterwheel by converting alternating current to direct current without using a PWM converter, the applicant of the present application had proposed an electric power generating apparatus for dispersed power supply comprising a permanent magnet type electric power generator including a plurality of windings inducing different induced voltages and having alternating current output terminals each connected in series through a reactor to a rectifier, and the direct current outputs of these rectifiers being connected in parallel to one another, thereby outputting the direct current external (refer to, for example opened Japanese Patent Literature 1).
Such a prior art technique will be explained in detail with reference to a main circuit diagram illustrating an electric power generating apparatus for dispersed power supply connected to a windmill shown in FIG. 13.
In FIG. 13, a windmill is denoted by reference numeral 1 and an electric power generating apparatus for dispersed power supply of the prior art is denoted by reference numeral 2 comprising a permanent magnet type electric power generator 3, first and second reactors 4 and 5, first and second rectifiers 7 and 8, a positive output terminal 11 and a negative output terminal 12. Reference numeral 13 denotes a battery.
The permanent magnet type electric power generator 3 in FIG. 13 has two kinds of windings and of a three-phase generator.
In the permanent magnet type electric power generator 3 in FIG. 13, connected, to the first reactor 4 and further to the first rectifier 7 is the alternating current output terminal W1 of a first winding whose effective value of induced voltage is low due to its smaller number of turns.
Connected to the second reactor 5 and further to the second rectifier 8 is the alternating current output terminal W2 of a second winding having a larger number of turns.
The direct current outputs of the first and second rectifiers 7 and 8 are connected in parallel to the positive output terminal 11 and the negative output terminal 12, and the total output of the respective windings is stored into the battery 13.
A method for obtaining the substantially maximum output from the electric power generating apparatus 2 for dispersed power supply thus configured will be described hereinafter.
FIG. 12 is a diagram for explaining the outline of the number of revolutions of the windmill versus output characteristic when wind speed is taken as the parameter.
With a windmill, if the shape of the windmill and wind speed U are determined, the output P of the windmill is monolithically determined with respect to the number of revolutions N of the windmill. For example, the output P of the windmill for the wind speeds Ux and Uy is illustrated as in FIG. 12, respectively. Peak values of the outputs P of the windmill for various wind speeds are shown as the maximum output curve Pt in FIG. 12.
In more detail, with the number of revolutions of the windmill versus output characteristic in FIG. 12, when the wind speed is Ux, the maximum output Px of the windmill is obtained at the number of revolutions Nx of the windmill as shown at the intersection point Sx of the windmill output curve at the wind speed Ux with the maximum output curve.
Moreover, when the wind speed is Uy, the maximum output Py of the windmill at the wind speed Uy is obtained at the number of revolutions Ny of the windmill.
Namely, when viewing the maximum output curve in FIG. 12 from another point, this curve indicates the fact that in order to obtain the maximum output from the wind, upon the number of revolutions N of the windmill being determined, the maximum output can be obtained by primarily determining the output P of the permanent magnet type electric power generator 3 at a value on the maximum output curve Pt.
FIG. 11 is an explanatory view when the direct current outputs of the electric power generating apparatus 2 for dispersed power supply of the prior art are connected to a constant voltage power supply such as a battery or the like. As shown in FIG. 11, respective outputs of the first and second windings of the permanent magnet type electric power generator 3 of the electric power generating apparatus 2 for dispersed power supply are shown as the number of revolutions of windmill versus output characteristic curves P1 and P2 owing to difference in the effective values of induced voltages of the windings and voltage drops caused by internal inductances of the respective windings and the reactors connected to the respective output terminals.
In other words, when the number of revolutions N of the windmill is low, the battery 13 is not charged because the induced voltages of the first and second windings in the permanent magnet type electric power generator 3 are lower than the battery voltage Vb.
However, when the number of revolutions N of the windmill increases to a value near to N2, the electric current starts to flow through the second winding. With increase in number of revolutions N of the windmill, the electric current increases so that the output of the second winding is as shown at P2.
At this time, even if the number of revolutions N of the windmill increase to cause the induced voltage to be increased, the voltage of the battery remains at substantially constant value. On the other hand, the output P2 only gradually increases because the inductance of the second winding and the inductance by the second reactor 5 are proportional to the frequency.
With the first winding, when the number of revolutions N is further increased, the output starts to be obtained and greater output can be obtained because the internal inductance of the first winding and inductance of first reactor 4 are both small.
FIG. 10 illustrates the output to a constant voltage power supply such as a battery of the electric power generating apparatus for dispersed power supply of the prior art.
A total output obtained by summing up the outputs P1 and P2 of the first and second windings in the permanent magnet type electric power generator 3 is shown by an approximate output curve Ps.
Patent Literature 1: Japanese Patent Application Opened No. 2004-64,928 (FIG. 1)